Investigation of plasmid DNA and antibiotic resistance in some pathogenic organisms

Twenty-eight strains of Salmonella, Pseudomonas, and Escherichia coli isolated from cultures of stool, urine and wound were tested for their susceptibility to various antimicrobial agents. All the strains were resistant to erythromycin and tetracycline. Nineteen Salmonella isolates were susceptible to chloramphenicol and gentamycin. All the Pseudomonas and Escherichia coli isolates were resistant to chloramphenicol and cloxacillin while one Pseudomonas species and three Escherichia coli isolates were sensitive to gentamycin. The antibiotic resistance determinants in each strain were encoded by plasmid. These isolates were typed by plasmid profile analysis according to their different molecular weights. Several similar and distinct profiles were identified for most resistant and sensitive isolates. It appeared that a single strain containing a plasmid conferring multiple drug resistance emerged within the bacterial population and was able to adapt and to survive the challenges of antibiotics as they were introduced into clinical medicine. Therefore, the acquisition of plasmid has greatly contributed to the rapid spread of antibiotic resistance genes in the bacterial population.